1. Field of the Invention
This invention generally relates to an informing apparatus for a vehicular cruise control system having at least one of an inter-vehicle control function and a basic cruise control function (a constant-speed travel control function). The inter-vehicle control function enables the present vehicle to automatically follow a preceding vehicle. The basic cruise control function enables the present vehicle to automatically travel at a setting speed. This invention particularly relates to an apparatus which is used together with a vehicular cruise control system, and which gives a user information related to a vehicle speed and employed in cruise control.
2. Description of the Related Art
Regarding automotive vehicles, cruise control systems have been developed as driver assistance systems. Cruise control systems include an inter-vehicle control system, a basic cruise control system (a constant-speed travel control system), and an advanced cruise control system. The advanced cruise control system has a combination of the inter-vehicle control system and the basic cruise control system (the constant-speed travel control system). The inter-vehicle control system enables the present vehicle to automatically follow a preceding vehicle at a speed in a given range. The basic cruise control system enables the present vehicle to automatically travel at a speed set by a user in a given range. During operation of the advanced cruise control system, the inter-vehicle control system can be active in the presence of a preceding vehicle while the basic cruise control system can be active in the absence of a preceding vehicle.
Such a cruise control system is allowed to start when the speed of the present vehicle is in a given range, specifically a range between a setting lower limit vehicle speed and a setting upper limit vehicle speed. It is known that the cruise control system is automatically suspended when the speed of the present vehicle drops below a lower side limit vehicle speed, that is, a lowest control-enabling vehicle speed.
In general, an advanced cruise control system is able to operate in an automatic cruise control mode. During the automatic cruise control mode of operation, change between inter-vehicle control and basic cruise control (constant-speed travel control) is automatically implemented. Specifically, during the execution of the inter-vehicle control, the speed of the present vehicle is controlled in a range lower than a setting speed, that is, a speed set by a user. In the absence of a preceding vehicle (a preceding control object), the speed of the present vehicle is increased to the setting speed and is then held equal to the setting speed by the basic cruise control.
A known means for informing a user of the transition between inter-vehicle control and basic cruise control includes a meter apparatus which indicates the presence and the absence of a preceding control object (a preceding vehicle). The information indicated by the meter apparatus makes it possible for the user to understand the reason why the speed of the present vehicle is increased in the absence of a preceding control object (a preceding vehicle).
SAE TECHNICAL PAPER SERIES 961010, "Adaptive Cruise Control System Aspects and Development Trends", discloses that a setting vehicle speed is indicated on a meter apparatus. The comparison between the setting vehicle speed and the speed of the present vehicle makes it possible to predict whether the speed of the present vehicle will be further increased or not.
Control parameters used by the inter-vehicle control system and the basic cruise control system include a setting lower limit vehicle speed, a setting upper limit vehicle speed, and a lower side limit vehicle speed (a lowest control-enabling vehicle speed). These control parameters are not displayed on an indicator although they are mentioned in a cruise control instruction manual.
A prior-art advanced cruise control system tends to give a driver the following unusual feelings 1 to 7.
1 During the execution of the inter-vehicle control, since the speed of the present vehicle is not further increased when the speed of the present vehicle has already reached a setting vehicle speed, there sometimes occurs a case where a preceding control object (a preceding vehicle) moves away from the present vehicle although the preceding control object is detected or captured in the inter-vehicle control. If the driver is not aware that the speed of the present vehicle has already reached a setting vehicle speed, the driver can not immediately understand the reason why the present vehicle is not accelerated to follow the preceding vehicle.
2 During the automatic cruise control mode of operation, the inter-vehicle control is replaced by the basic cruise control when any preceding control object (any preceding vehicle) is not captured. The speed of the present vehicle will not be increased further when the speed of the present vehicle has already reached a setting vehicle speed. If the driver is not aware that the speed of the present vehicle has already reached the setting vehicle speed, the driver can not immediately understand the reason why the speed of the present vehicle is not increased. In some cases, the driver erroneously considers this phenomenon to be caused by the capture of a new preceding control object (a new preceding vehicle). In these cases, the driver feels a reduction in reliability of the control system.
3 During the automatic cruise control mode of operation, the basic cruise control is implemented when any preceding control object (any preceding vehicle) is not captured. In this case, the speed of the present vehicle can be increased to a setting vehicle speed. If the driver does not understand the relation between the speed of the present vehicle and the setting vehicle speed, the driver tends to wonder what speed the present vehicle will be accelerated to.
4 Regarding either the inter-vehicle control or the basic cruise control, a setting vehicle speed can not be given unless the speed of the present vehicle is equal to or higher than the setting lower limit vehicle speed. If the driver does not understand this fact and tries to give a setting vehicle speed when the speed of the present vehicle is lower than the setting lower limit vehicle speed, the driver wonders why the setting vehicle speed can not be given.
5 The inter-vehicle control is automatically canceled when the speed of the present vehicle drops below the lower side limit vehicle speed (the lowest control-enabling vehicle speed). If the driver is not aware that the inter-vehicle control has been canceled, the driver tends to think why the present vehicle does not follow a preceding vehicle (a preceding control object). If the driver does not understand the lower side limit vehicle speed (the lowest control-enabling vehicle speed), the driver tends to be anxious about how much drop in the speed of the present vehicle will cause the cancel of the inter-vehicle control.
6 During the execution of either the inter-vehicle control or the basic cruise control, if the driver is not aware that the speed of the present vehicle has already reached the setting upper limit vehicle speed, the driver may try to increase a setting vehicle speed.
7 In the case where a target control amount is small, a variation in behavior of the present vehicle is also small while a meter indicating the speed of the present vehicle only slightly moves. In this case, it is sometimes difficult for the driver to decide whether the control system is operating normally. Thus, the driver may feel uneasy about the control system.
The causes of these problems are as follows. A prior-art meter indicator displays information of the speed of the present vehicle, information of a setting vehicle speed, and information of the presence and the absence of a preceding control objet (a preceding vehicle). In general, the prior-art meter indicator does not display information related to vehicle speeds such as a setting lower limit vehicle speed, a setting upper limit vehicle speed, and a lower side limit vehicle speed (a lowest control-enabling vehicle speed). The setting lower limit vehicle speed, the setting upper limit vehicle speed, and the lower side limit vehicle speed (the lowest control-enabling vehicle speed) are mentioned in a cruise control instruction manual. Thus, a user is required to understand states of inter-vehicle control and basic cruise control in consideration of a lot of information.
The behavior of the present vehicle dynamically changes in response to a variation in environments surrounding the vehicle. The cause of a change in the behavior of the vehicle can be known by looking at a meter indicator. It is troublesome for a driver to look at a meter indicator each time a change in the behavior of the vehicle occurs. Also, it is troublesome for the driver to previously memorize vehicle speed information which is not displayed on the meter indicator. In some cases, driver's judgment based on a scene in front of the driver is inconsistent with a change in the behavior of the vehicle. Such an inconsistency may cause the driver to make a wrong decision.
The causes of the previously-mentioned driver's unusual feelings are that pieces of much information exist in different forms respectively.